Hesaraghatta Catchment Timeseries Analysis

Hesaraghatta Catchment 122-Yr Rainfall Analysis (1901-2022)

Updated Date: 11 Feb 2024

Outline:

Executive Summary
Analysis of 122 years of IMD’s rainfall data for period 1901-2022 for the following Seasons:
1. Annual
2. Both monsoons combined Jun-Dec
3. South-west monsoon Jun-Sep
4. North-east monsoon Oct-Dec
5. Pre-monsoon Mar-May
6. Dry season Jan-Feb

Information on some of the key terms used can be found here

Executive Summary

The annual and monsoon rainfall data reveals that both 2021 and 2022 marked record-breaking years in the span of 122 years, as illustrated in the accompanying table to the left.

1. Annual Rainfall Timeseries (1901 – 2022)

In 2022, the Hesaraghatta catchment experienced unprecedented rainfall of 1568mm, setting a new record, as depicted in Graph 1 below. The year 1985 is the driest year, with a meagre 360mm.

Graph 1 identifies the top ten high-rainfall years. Seven of the top ten occurred post-1990, with five occurring after 2009. Additionally, out of 122 years, 20 experienced rainfall exceeding 1000mm, with 14 occurrences observed after 1971. This indicates recent intensification and aligns with rising CO2 levels marked on the graph, suggesting a link between climate change and changing precipitation patterns.

Graph 1: Annual Rainfall Timeseries (1901 -2022)

With a recorded rainfall of 1568mm, 2022 marked a remarkable 98% departure from the Indian Meteorological Department’s (IMD) normal of 791mm. 2022 also deviated by 93% from the World Meteorological Organization’s (WMO) normal of 814mm. The IMD’s current normal of 791mm is based on the 50-year LPA from 1991-2020, while WMO’s normal of 740mm is based on the 30-year LPA from 1991-2020.

It can be observed from Table 1, that the percentage of departures in 2022 far exceeds any other year on record.

Table 1: Top Ten High Rainfall Years and % Departures

2. Jun-Dec Monsoon Rainfall Timeseries (1901 – 2022)

The monsoon of 2022 recorded 1263mm of rain, a 94% deviation from normal, breaking all previous records and marking the highest rainfall in 122 years. Additionally, 2021 also had record-breaking rainfall with 1118mm, 72% above normal, making it the second-highest rainfall in 121 years after 1903, as depicted in Graph 2 below. The year 2002 is the driest year, with a meagre 244mm.

Graph 2 identifies the top ten high-rainfall years. Five of the top ten occurred post-1990, and four of them occurred before 1913.

Graph 2: Jun-Dec Monsoon Rainfall Timeseries (1901 -2022)

With a recorded rainfall of 1263mm, 2022 marked a remarkable 94% departure from the IMD’s normal of 650mm. Similarly, 2022 deviated by 91% from the WMO’s normal of 662mm. The IMD’s current normal of 650mm is based on the 50-year LPA from 1991-2020, while WMO’s normal of 662mm is based on the 30-year LPA from 1991-2020.

It can be observed from Table 2, that the percentage of departures in 2022 far exceeds any other year on record.

Table 2: Top Ten High Rainfall Years and % Departures

3. Jun- Sept Southwest Monsoon Rainfall Timeseries (1901 2022)

In 2022, the Hesaraghatta catchment experienced unprecedented southwest rainfall of 918mm, setting a new record, as depicted in Graph 3 below. The driest year on record occurred in 2002, with a meagre 135mm.

Graph 3: Jun-Sep Southwest Monsoon Rainfall Timeseries (1901 -2022)

With a recorded rainfall of 918mm, 2022 marked a remarkable 108% departure from both IMD and WMO normal of 441mm.

The accompanying Table 3 highlights the top ten high rainfall years and their departures, showing that the percentage departure of 2022 surpasses all others.

Table 3: Top Ten High Rainfall Years for Southwest and % Departures

4. Oct-Dec Northeast (Post-monsoon) Monsoon Rainfall Timeseries (1901-2022)

In 2021, the Hesaraghatta catchment experienced unprecedented northeast monsoon rainfall of 569mm, setting a new record, as depicted in Graph 4 below. The driest year on record occurred in 1959, with a meagre 29mm.

Graph 4: Oct-Dec Northeast Monsoon Rainfall Timeseries (1901 -2022)

With a recorded rainfall of 569mm, 2021 marked a remarkable 172% departure from IMD’s normal of 209mm. Similarly, it marked a 157% departure from WMO’s normal of 221mm.

The accompanying Table 4 highlights the top ten high rainfall years and their departures, showing that the percentage departure of 2021 surpasses all others.

Table 4: Top Ten High Rainfall Years for Northeast and % Departures

5. Mar-May Pre-monsoon Rainfall Timeseries (1901-2022)

In 2011, the Hesaraghatta catchment experienced unprecedented pre-monsoon rainfall of 333mm, setting a new record, as shown in Graph 5 below. The second-highest was recorded in 2022 at 303mm. Both 2022 and 2011 are the only two years in the 122-year rainfall history with over 300mm.

The driest year on record is 1906, with a meagre 19mm.

Graph 5: Mar-May Pre-monsoon Rainfall Timeseries (1901 -2022)

The 2011 rainfall of 333mm marks a 159% departure from IMD’s current normal of 133mm and a 128% departure from WMO’s current normal of 145mm.

Table 5 illustrates the top ten rainfall years and their departures, showing 2011’s substantial deviation from normal.

Table 5: Top Ten High Rainfall Years for Pre-Monsoon and % Departures

6. Jan-Feb Dry Season Rainfall Timeseries (1901-2022)

In 1908, the Hesaraghatta catchment experienced 104mm, the highest of 122 years. The IMD normal is 8mm and WMO normal is 6mm as can be seen from Graph 6 below.